The main objective is to clarify the mechanism by which latent infection membrane 1 (LMP1) transduces signals that transform B-cell growth because this will provide insight into targets for development of inhibitors for treating Epstein-Barr virus (EBV) related malignancies. EBV is a principal cause of an opportunistic lymphoma in immune compromised patients and is etiologically associated with Hodgkin's lymphoma, Burkitt's lymphoma, and nasopharyngeal carcinoma. These cancers are particularly problematic because EBV infects most humans for a lifetime. EBV persists by infecting B-cells as a latent virus to evade host immunity and by expressing proteins such as LMP1 that transform B-cells into long-term proliferating cell lines. This proposal's main hypothesis is that LMP1 is an oncogenic plasma membrane receptor whose C-terminal tail continuously recruits cytoplasmic adapters that usurp the TNFR (tumor necrosis factor receptor) signaling pathway and thus critically alters gene transcription that drives cells to proliferate. This hypothesis is based upon several observations. 1) LMP1 is required for EBV to transform B-cell growth. 2) LMP1 spontaneously forms plasma membrane aggregates that continuously activate NF-KB transcription factors by recruiting ubiquitin-activating E1-like protein (UBE1L), TNFR associated factors (TRAFs), TNFR associated death-domain protein (TRADD), or receptor interacting protein (RIP). 3) TRAFs, TRADD, and RIP activate NF-KB by targeting I-KB inhibitors for ubiquitination and proteasome destruction. 4) UBE1L catalyzes an early step in a ubiquitin-like activation cascade. Based on these observations, the goal is to delineate the mechanism by which LMP1 utilizes UBE1L to usurp TNFR-signaling pathways to transform B cell growth. The specific aims are to: 1) Investigate the interaction of LMP1 with UBE1L and the effects of this interaction on NF-KB activation. 2) Clarify the role of LMP1 recruitment of UBE1L in B-cell transformation by molecular analyses of EBV recombinants that are blocked for UBE1L recruitment. 3) Analyze the proteins recruited to the LMP1-UBE1L signaling complex and investigate their role in NF-KB activation and B-cell transformation. The results of these analyses are important because delineation of LMP1 associated signaling effectors that mediate B-cell transformation is a first step toward the development of specific inhibitors that may be used to prevent or treat EBV-related malignancies.